The invention relates to coarse or fine grained thermoplastic base resin-dyestuff concentrates and their manufacture.
Thermoplastic base resins normally are furnished to the manufacturer of the final products of synthetic plastic materials in an undyed condition as a powder or granulate. The dyeing of the plastic resins for making colored products is then effected usually by adding the dyestuffs to the thermoplastic base resin hereinafter referred to simply as "resin," prior or during the introduction into the molding or similar machine, for instance an injection mold, a kneader or an extruder. This procedure frequently fails to lead to a complete mixing of the dyestuff with the resin. The dyeing of the product therefore is frequently obtained in a non-homogeneous speckled way.
The industry therefore prefers to use concentrates of dyestuff and resin for the dyeing of synthetic plastic material. In these concentrates, resins are intimately blended with large amounts of a dyestuff. The resin then acts in the resin-dyestuff concentrate as a kind of solution promoter between the dyestuff and the undyed "dilution" resin to be colored, thereby providing a homogeneously dyed product.
The making of the resin-dyestuff concentrates, which are also called "master batches", is done in a manner similar to the dyeing of thermoplastic resins with dyes, in injection molds, leaders or extruders, except that a particularly high ratio of dyestuff to resin is necessary and the blended material is eventually comminuted to a granulate.
It is evident that this kind of manufacture of resin-dyestuff concentrates is practical only for large amounts. For making smaller amounts of a specific dye color this process is uneconomical since the injection molds, extruders and kneaders can be operated economically only with large throughputs of materials.
It is therefore an object of the invention to provide for an economical way to form resin-dyestuff concentrates from inorganic or organic dyestuffs. It will be understood that the term "dyestuff" in this connection also includes the inorganic pigments.